Vitamin D may be one of the most fundamentally important building blocks available to us for creating and sustaining vibrant health (1). Vitamin D promotes calcium absorption in the intestine and maintains calcium and phosphate levels in the blood, protecting against osteoporosis, rickets, and bone fracture. It also regulates immune function, cell growth, inflammation, and neuromuscular function (2). And before we get much further, it’s interesting to call out: vitamin D in its active form is actually a hormone! Despite the original misnaming as a vitamin, it continues to be called ‘vitamin D’ (3).
Vitamin D is complex and requires other synergistic nutrients to be utilized in our bodies. For starters, vitamin D is fat-soluble, meaning, fat is a necessary vehicle for vitamin D to be absorbed. Another example is vitamin D’s role in building and maintaining healthy bones. While calcium is the primary component of bone, it can only be absorbed by your body when vitamin D is present (4). Another complex relationship is between the fat-soluble vitamins, A, D, and K. Vitamin A is an essential factor in vitamin D’s hormonal function, and vitamin K is necessary to activate the proteins made in response to vitamins A and D (5).
Recommendations for what constitutes adequate intake of vitamin D varies, but it’s estimated that 70% of the population doesn’t get enough (6). Nutritional biochemist Dr. Chris Masterjohn has presented evidence suggesting that optimal vitamin D levels may vary from population to population. One must also take into consideration other vitamin deficiencies and lifestyle factors that may play a role in your overall vitamin D need.
There are three ways to obtain vitamin D: exposure to sunlight, food, and supplements. The most effective of all of these methods is exposure to sunlight. Your body makes vitamin D when direct sunlight converts a chemical in your skin into an active form of the vitamin (7). There are some limiting factors, however, such as location, time of year, skin pigmentation, age, pollution, and application of sunscreen. Due to these varying factors, it’s challenging to state a general amount of time one must spend outside. A great, free app, to learn how much time to spend in the sun depending on your age, skin color, and location is D minder!
The next best source of vitamin D is obtained from whole foods. In comparison to other nutrients, the list of vitamin D containing foods is quite short. According to The World’s Healthiest Foods, wild-caught salmon is the best food source of vitamin D as a single serving contains more than the generally suggested Daily Value (DV). Sardines contain over 40% of the DV, and tuna contains just under 25%. Pasture-raised eggs are a good source of dietary vitamin D, with about 10% of the DV per egg. The vitamin D is found in the yolk, so reason number 57 to eat the yolks! Some mushroom species, including shiitakes, contain as much as 5% of the DV (8).
You may be asking, “why isn’t milk on this list? I always see ‘fortified with vitamin D’ on the container?!” This is where things get tricky. While milk does supply a high dose of vitamin D, I want to provide a caveat when relying on processed foods to meet your vitamin and nutrient requirements.
In the United States, as in most parts of the world, fortification of food was initiated as a systematic approach to correct the identified nutrient deficiencies in the population (9). The problem with fortification is that the body does not absorb individual nutrients added to processed foods as efficiently compared to nutrients naturally occurring in whole foods (10). Whole foods contain synergistic nutrients that work together to enhance the bioavailability and utilization of each other in our bodies. For example, any milk that has been processed to remove the fat loses the fat-soluble vitamins A, D, and K. Although vitamins A and D are added back, our bodies cannot absorb them without a fat vehicle, nor can they function optimally without the assistance of vitamin K (11). Through this processing of the milk, we’re losing vital nutrients.
With all of that being said, milk does provide vitamin D, however, sourcing is very important. Ensure that your milk is from pasture-raised, organic, grass-fed cows that have ample access to the outdoors and sunlight, as their milk may contain vitamin D even if non-fortified (12).
Rounding this all out, the very best way to obtain vitamin D is to get plenty of sunlight combined with a nutrient-dense, whole foods diet. However, our modern sedentary and mainly indoor lifestyle, combined with a heavy reliance on processed foods has left the majority of Americans deficient in this vital nutrient. If after proper testing it is determined that you are deficient in vitamin D, a recommended source of supplementation is Thorne D/K2 drop (no affiliation, I just trust the brand) as it provides the co-factors needed for adequate utilization of the vitamin. While vitamin D is generally regarded as safe, always consult with your doctor before considering the use of any Vitamin D supplement, especially if you have health conditions or diseases that need to be addressed or are pregnant or breastfeeding.
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Masterjohn, Christopher. “From Seafood to Sunshine: A New Understanding of Vitamin D Safety.” The Weston A. Price Foundation, 10 Feb. 2020, www.westonaprice.org/health-topics/abcs-of-nutrition/from-seafood-to-sunshine-a-new-understanding-of-vitamin-d-safety/.
Kresser, Chris. “Vitamin D: More Is Not Always Better.” Chris Kresser, 4 Sept. 2019, chriskresser.com/vitamin-d-more-is-not-better/.
Morris, Howard A. “Vitamin D: a Hormone for All Seasons--How Much Is Enough?” The Clinical Biochemist. Reviews, U.S. National Library of Medicine, Feb. 2005, www.ncbi.nlm.nih.gov/pmc/articles/PMC1240026/.
“Vitamin D.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 18 Oct. 2017, www.mayoclinic.org/drugs-supplements-vitamin-d/art-20363792.
Masterjohn, “From Seafood to Sunshine.”
Ballantyne, Sarah. “Paleo Principles”, Victory Belt Publishing Inc. 2017.
“Vitamin D”, Mayo Clinic.
“Vitamin D.” The World's Healthiest Foods, whfoods.com/genpage.php?tname=nutrient&dbid=110.
Institute of Medicine (US) Committee on Use of Dietary Reference Intakes in Nutrition Labeling. “Overview of Food Fortification in the United States and Canada.” Dietary Reference Intakes: Guiding Principles for Nutrition Labeling and Fortification., U.S. National Library of Medicine, 1 Jan. 1970, www.ncbi.nlm.nih.gov/books/NBK208880/.
“Dangers of Food Fortification and Enrichment.” Elmhurst 1925, elmhurst1925.com/blogs/news/dangers-of-food-fortification-and-enrichment.
Albahrani AA, Greaves RF. Fat-Soluble Vitamins: Clinical Indications and Current Challenges for Chromatographic Measurement. Clin Biochem Rev. 2016;37(1):27-47.
“Vitamin D.” The World's Healthiest Foods.